Sumbawa can have shifty winds especially in august.
East sumbawa- lakey peak will be onshore almost all the time. you might be able to find somewhere protected but they are not worth travelling to.
West sumbawa is fickle and some breaks are offshore in the trades but they are more often onshore with SW winds especially on the bigger days. Also most of the people who go to this area are agro hardcore surfers. and some kooks dropping in. Better places to go include g-land which is offshore almost everyday in august. but you have to be able to surf.